Check Engine Light on

I purchased a 96 GC with a V8 5.2 L 4X4 a month ago. It was running very well. However, the check engine light came on after I change Oil and Oil filter at the Dodge dealer. The error codes are 12-51-55. What the error codes mean? I noticed my gas mileage gets really low. Does it anything to do with? And how to fix it? Could it be the O2 sensors problem? Please help.

12 Battery disconnected. Battery or power to the ECM disconnected in the last 50 key cycles

51 O2 detects lean mixture. Check sensor and circuit and for vacuum leaks.

55 End of code. Trouble codes finished or none recorded.


looks like all you have as a problem is the 51

I finally remove the old O2 sensor from my 96 JGC and it runs much better. However, the check engine is still on and now it has 12 21 55 message codes. So, what is this "21" mean and how to fix it? Thanks.

21 Oxygen sensor or circuit. O2 sensor or wiring faulty.


did you remove the power from the batt . to reset all the codes.
if you do you should only get a
12 Battery disconnected. Battery or power to the ECM disconnected in the last 50 key cycles
and
55 End of code. Trouble codes finished or none recorded.

make sure the new o2 wire is pluged in good.

good luck
steve lock

Thanks steve lock

I'll check again. Thanks for your help.

Rw0623